You’ve almost certainly heard about red-green color blindness. It’s terribly common – in occurs in ~8% of European men. That is a surprisingly high frequency for a genetic problem, but the fundamental cause is a weirdly high mutation rate, due to the fact that the genes for the red and green cone pigments are right next to each other on the X chromosome and often get scrambled in recombination. Even in this case, though, natural selection matters: deuteranopia is less common outside of Europe, sometimes far less common. About 5% of men in China have it, while about 1% of Pygmies do. The suspicion is that it matters less among farming peoples than in hunter gatherers, and thus is more common in people who have been farming longer, least common in people who are still foragers.

There is an interesting riff on this: some of the scrambled versions of the red and green genes still work, but have slightly nonstandard absorption spectra. So there are a number of slightly different green and red genes – and women, with two X chromosomes, can have four different color sensors, instead of the standard three. There is something similar in New World monkeys, where males have two working cone pigments and females often have three.

Usually the brain wiring doesn’t seem to support four color vision in women who are tetrachromats, but at least one case exists. Most people can distinguish about 1 million different color, but she can probably distinguish 100 million. She can see things no else can see, without taking a potion.

In principle one could push this farther by putting contact lenses with different filters in each eye, so that the left eye saw the bottom half of red and the right eye the top half: ordinary people could in principle distinguish six colors, while that tetrachromat lady could distinguish eight. But it might screw up your depth perception, you’d likely get a headache, and, as my real analysis prof said (Wolfgang Haken), four colors suffice.

You probably know of color-blind men who have someone else help them pick out clothes: they can’t tell, but most other people can. The lady who is a working tetrachromat could give you better advice on how things really look, but she’s one of the very few people who could appreciate the effect. But doesn’t that make it even classier?

I mean, audiophiles have been known to shell out lots of money for highly linear audio systems – when they can’t hear the difference. Personally, I used to subscribe to Low Fidelity, because I loved those analytical articles about taping a quarter on the tone arm, recording AM music during a thunderstorm, and saving audio system money by repeatedly hitting a roll of caps with a hammer on the Fourth – but not everyone is like me.

The story is similar, but more complicated, with olfactory receptors. There are about 400 working olfactory receptors in humans, but many of them have multiple versions, including pseudogenes – rather like red-green color blindness, only there are 400 detectors involved instead of 3, and 70 of them work in some people but not everyone. And, like color blindness, the frequency of these non-working versions varies between populations. In those olfactory genes that have working and nonworking versions, Pygmies seem to have higher frequencies of the working versions than Europeans do, just as they are less likely to be color blind. Probably the sense of smell works better in the rain forest (moist air) and it may be that the ability to recognize certain specific scents, such as that of a lion hiding in the bushes nearby, has survival value.

There are so many possible combinations of working and nonworking olfactory genes that very few people, maybe no-one other than identical twins, share the same set of smell receptors. This explains otherwise inconceivable things, such as people who like broccoli. They taste a different world.

If Pygmies do have a significantly higher fraction of working olfactory genes, probably some Pygmies have a better sense of smell than any European. It might be that the average Pygmy has a better sense of smell than any European. And this suggests a new career path for the Pygmy race.

Right now Pygmies are taking it in the shorts. They are often enslaved, always discriminated against, sometimes eaten. They need to find a new way. If I’m right, their natural new niche is as super-sommeliers. They’ll know more about wine than you ever will: you’ll never be able to taste what they taste. Reminds me of a televised Beethoven concert at Wolf Trap where an interpreter was signing for the hearing-impaired: I figure he was saying “This shit is great, but you’ll never know, because you’re fucking deaf!”

Once they learn the patter and the necessary arrogance – once we teach them to look down on customers while looking up at them – they’ll be a shoo-in. It will be as big a success as Neanderthal gaming. Every five-star restaurant will have one.

You don’t know you’re colorblind unless someone tells you. I have a mild red/green colorblindness that makes most pinks and some greens and blues wash out to shades of gray. I thought our house was gray (it was blue) and our curtains were gray (they were green). When someone points out the correct color some of the time I can ‘see’ it. It’s hard to explain but sometimes I can actually see it as the right color (a really grayish pink, green, or blue) and other times I can ‘see’ that the way I am looking at is wrong and guess what other folks are seeing. Dim light and or distance makes it harder.

I had no idea I was colorblind until someone gave me a test when I was eleven. My uncle has severe red/green colorblindness and on his first date with his ex-wife he showed up in a purple shirt and green pants. He thought they matched.

I once read a wonderful article — I think it was in Scientific American, but I’m not sure — about color vision in tetrapods. As I recall, the thesis was that tetrapods originally inherited four color receptors from their fishy ancestors, and that most amphibians, reptiles, and birds still have the original four. Further, there were diagrams showing how the peak sensitivities of the four receptors were very evenly spaced out across the spectrum between red and ultraviolet.

However mammals, because of their nocturnal habits, lost two of those receptors. And while primates managed to regain one, they did so by duplicating an existing receptor, and the peak sensitivities of the original and the duplicate are still rather close. As a result, not only do birds, for example, have much better color vision than we do, as a result of having four receptors rather than three, but they also have the additional advantage that their receptors cover the spectrum in a more efficient manner. This would imply that the color vision of birds would far outstrip even that of the tetrachromat lady.

Does this ring a bell with anyone? I’d like to read that article again, but I haven’t been able to find it.

Here is a recent podcast by Radiolab about all this, mentioning the search for the tetrachromat lady , the mantis shrimp (16 color receptors), and the technical possibility of getting the fourth cone in our eyes through bioengineering. It is quite entertaining.http://www.radiolab.org/2012/may/21/

There was such a Sci. Am. article. But this reminds me that there’s a theory out there that the differentiation between the red and green receptor in primates was due to a specific pressure: Red and Green are quite close on the spectrum, but having two receptors with those two close peaks is very useful for discerning the ripeness of fruit. That is, whether it’s worth the effort to climb the tree to grab it. And one of the “channels” via which the retina reports color to the brain is the difference between the Red and Green receptors, so the nervous system reports differences in that narrow slice of the spectrum efficiently.

Which may account for why color blindness is particularly selected against in Pygmies.

Some people really lack big important chunks of the nervous system. Certainly broccoli is one of the finer things on the table. But inability to love broccoli certainly pales in comparison to the tragedy endured by people who do not love blazing hot chili. Imagine, for example, someone living in New Mexico who could not tolerate hot chiles. What would be the worth of such a life?

Under such circumstances a sane person would pray for the sweet oblivion that only death could bring. More seriously–there is some annecdotal evidence that red/green CB spotters were actively sought by night bomber crews as having better night vision. This might happen with a gendered shared labour in other primates too?

I’ve heard stories that men with non-standard red/green receptors (phenotypically, with partial color blindness) were used to spot camouflage — because color-matching with paint works differently in their eyes.

It seems to me that taster differences are not so much differences in olfaction but which bitter receptors you have. There are something like 25 different human bitter receptors, but they all produce the same sensation. Which subset you get is going to strongly affect your taste preferences.

Off topic request for Greg Cochran,
Greg, I would be really interested in your thoughts on our experience of free will and whether it’s compatible with the laws of cause and effect that seem to operate everywhere except in our brains.
Thanks

The color channels run blue/yellow, and red/green (which is why you can have a bluish-red (purple), bluish green (aqua), yellowish red (orange), and yellowish green (lime), but not a bluish yellow or reddish green). I was thinking that the reason for the blue/yellow and red/green channels was that our primitive ancestors living on the edge of the savannah looking out would need to distinguish the savannah (yellow) from the sky (blue), and looking back into the forest would need to discriminate the trees (green) from their fruit (red). Do you know if this theory has been offered anywhere?

Well, we have three cones, red, green and blue. The colors we can see are determined by their combination. We can actually have a bluish yellow (green), and a reddish green (yellow or orange, depending on the red/green ratio). You can confirm this by projecting pairs of monochromatic lights of the colors I mentioned in a white surface. Oils or watercolors won’t work because they are not pure.

Daniel Lieberman’s Evolution of the Human Head went into some interesting detail about the evolution of human olfactory receptors – it seems that it’s more the case that humans, relative to other species and our ancestors, have more deactivated olfactory receptors in ways that reflect general environmental sense, but may be enriched at receptors which are related to foods, and also that humans (and primates) have less redundant and resilient olfactory systems, more than weaker ones (because they do not expose their noses to as much in the way of bacteria compared to say, dogs or mice).

Pygmy super sommeliers may be a matter of what olfactory abilities they are enriched for…. Wine does not taste of lion!

Reminds me of a televised Beethoven concert at Wolf Trap where an interpreter was signing for the hearing-impaired: I figure he was saying “This shit is great, but you’ll never know, because you’re fucking deaf!”

What I mean is that a tetrachromat would see distinctions in the real world which could not be reproduced on an RGB screen, and that therefore the colors on an RGB screen wouldn’t look quite right — just as an RB screen would be good enough for someone who was red-green colorblind but wouldn’t be able to display images that would look realistic to a trichromat.

Colour discrimination does not work uniformly – each one has frequency that is unable to sense without being totally colourblind. The same in olfactory senses: there are some volatile molecules they cannot capture. Strange as it may seem, many people with bad body odour are unaware that they smell. Their nostrils may be able to register the delicate fragancy of a rose but of smell of a rose but not the smell emanating from their armpits. Ainu and pygmy are unemployable as sommeliers in fancy restaurants, and now that you mention it, even as food they need to be marinated.

Pygmies, like other people descended directly from hunter gatherers, appear to be particularly susceptible to alcoholism.

Maybe among the original humans almost everyone was alcoholic, but with little or no alcohol available, it caused no harm. Maybe when farming led to the production of large amounts of alcohol the minority of people who were not naturally alcoholic had a big advantage and a much better change of surviving. So among people who are descended from farmers alcoholism is less common.

Canadian aboriginal people have a terrible problem with alcohol. But it is taboo to mention it unless you attribute the alcoholism to residential schools, or colonialism. But the fact is the aboriginal people probably have a genetic tendency towards addiction. How will we ever find a way to cure alcoholism if it is taboo to even talk about it in a reasonable way?

A dislike of broccoli might be more related to taste than smell. People differ in their sensitivity to bitter tastes (for example PTC). Then there is the case of cilantro, which tastes disgusting to some people but not others.

I remember hearing a theory that because macrobats are trichromatic (unlike microbats) they clade with us, and similarly we are less related to dichromatic monkeys. All the evidence for standard clustering was dismissed as convergent evolution (which seems a fine explanation for trichromatism). German Dziebel references it as a parallel to his out-of-America theory, which I can’t say does him any favors.

I reference it as parallel to out-of-America I (modern humans from New World primates). I personally don’t support it, but such notable homoplasies as pair bonding, cooperative breeding, reciprocal altruism and even rudiments of speech (babbling, etc.) can be marshaled in its support. Great apes don’t have them and it’s not easy to reconstruct how these interrelated traits emerged in the Homo lineage and became so vital to our species.